Oxidative dehydrogenation of monoolefins



3,322,347 OXHDATIVE DEHYDROGENATKON 6F MONOOLEFHNS James L. Callahan,Bedford, and Joseph J. Szabo, Chagrin 7 Claims. (Cl. 260-680) This isdivision of application Ser. No. 395,978, filed Aug. 19, 1964, now US.Patent No. 3,280,166 which is a division of application Ser. No.197,932, filed May 28, 1962, now US. Patent No. 3,186,955.

This invention relates to an improved oxidation catalyst consistingessentially of oxides of the elements bismuth and molybdenum, andoptionally, phosphorus, promoted by oxides of barium and silicon, and tothe catalytic oxidation of olefins to oxygenated hydrocarbons such aspropylene to acrolein, and the catalytic oxidative dehydrogenation ofolefins to diolefins such as butene-l to butadiene, and tertiaryamylenes to isoprene, and to the oxidation of olefin-ammonia mixtures tounsaturated nitriles such as propylene-ammonia to acrylonitrile, usingsuch catalysts.

The Callahan, Foreman and Veatch US. Patent No. 2,941,007 describes theoxidation of an olefin such as propylene and the various butenes withoxygen and a solid catalyst composed of the oxides of bismuth,molybdenum and silicon, and optionally, phosphorus. This catalystselectively converts propylene to acrolein, isobutylene to methacrolein,aand fi-butylene to methyl vinyl ketone and to butadiene, etc. Highyields are obtainable, although in the case of the butenes, carefulcontrol of reaction conditions may be required in order to direct thereaction in favor of either methyl vinyl ketone or butadiene, dependingupon which of these alternative products is desired.

The Idol, US. Patent No. 2,904,580, employs the same catalyst to convertpropylene, ammonia and oxygen to acrylonitrile, at approximatelyatmospheric pressures and elevated temperatures. Excellent conversions,usually in the range of 40 to 80%, nitrogen basis, of useful productsare obtainable.

I. THE CATALYST In accordance with the instant invention, the catalyticactivity of such bismuth oxide-molybdenum oxide catalysts is greatlyenhanced or promoted by the combination therewith of a mixture of bariumand silicon in the form of their oxides, referred to hereinafter aspromoters. The promoters in accordance with the invention are bestapplied by impregnation or surface coating of the catalyst, after itsformation in accordance with the procedure described in application Ser.No. 851,919 filed Nov. 9, 1959, now US. Patent 3,044,966, the disclosureof which is hereby incorporated by reference. Further, in accordancewith the invention, it has been determined that phosphorus oxide canalso be present as a supplemental oxide.

The proportions of barium oxide and silicon oxide, with or withoutphosphorus oxide and/or manganese oxide, are important in obtaining theoptimum enhanced activity. The barium oxide concentration, calculated asbarium, should be within the range from about 1 to about by weight; andthe amount of silicon oxide, calculated as silicon, should be within therange from about 3,322,847 Patented May 30, 1967 1 to about 10% byWeight, although more than 10% can be used, if desired.

While the catalyst of this invention may be employed without anysupport, it is desirable to combine it with a support. A preferredsupport is silica because the silica improves the catalytic activity ofthe catalyst. The silica may be present in any amount but it ispreferred that the catalyst contain between about 25 to by weight ofsilica. Many other materials such as alundum, silicon carbide,alumina-silica, alumina, titania and other chemically inert materialsmay be employed as a support which will withstand the conditions of theprocess.

The catalyst may comprise phosphorus, also present in the form of theoxide. Phosphorus will affect, to some extent, the catalytic propertiesof the composition, but the presence or absence of phosphorus has noappreciable effect on the physical properties of the catalyst. Thus, thecomposition can include from 0%, and preferably from at least 0.1%, upto about 5% by weight of phosphorus oxide, calculated as phosphorus.

The promoter is incorporated with the catalyst base by impregnationthereof, using an aqueous solution, dispersion, or suspension of abarium compound and of a silicon compound, either the oxide, or acompound thermally decomposable in situ to the corresponding bariumoxide or silicon oxide, respectively, without formation of otherdeleterious metal oxide residue, for instance, barium acetate,fluosilicic acid, barium bromide, barium chloride, barium nitrate,barium peroxide, barium persulfate, barium propionate, silicofluoride,sodium silicate, potassium silicate, hydrous barium silicate, silicicacids, such as monosilicic acid and polysilicic acids of low molecularweight, hydrous silica and colloidal silica. After impregnation withsuch solution, employed in a concentration and amount to provide thedesired amount of barium and silicon, the catalyst base is dried, andthen calcined at a temperature above that at which the compounds appliedare decomposed to the oxides. Temperatures in excess of 800 F. but belowthat at which the catalyst is deleteriously affected, usually not inexcess of about 1050 F., can be used.

The basic catalyst composition comprises bismuth oxide and molybdenumoxide, the bismuth-to-molybdenum ratio BizMo being controlled so that itis at all times above 1:3. There is no critical upper limit on theamount of bismuth, but in view of the relatively high cost of bismuthand the lack of an improved catalytic effect when large amounts areused, generally the atomic ratio bismuth to molybdenum Bi:Mo of about 3:1 is not exceeded. The nature of the chemical compounds which composethe basic catalyst is not known. The catalyst may be a mere mixture ofbismuth and molybdenum oxides, with or without phosphorus oxide, but itseems more likely that the catalyst is a homogeneous micro mixture ofloose chemical combinations of oxides of bismuth and molybdenum, with,optionally, phosphorus, and it is these combinations which appear toimpart the desirable catalytic properties to this catalytic composition.The catalyst can be referred to as bismuth molybdate, or, whenphosphorus is present, as bismuth phosphomoly-bdate, but this term isnot to be construed as meaning that the catalyst 15 composed of thesecompounds.

The barium and silicon compounds added thereto as promoters may or maynot enter into the chemical composition of the catalyst. Silicon addedlater with barium produces a different result from silicon added to acatalyst composition as a support and has a different function, sincethe enhanced catalytic effect is not obtained when silicon oxide iscombined as a support. Hence, the promoted catalytic efiect may be dueto some complex silicon oxide-barium oxide combination formed on thesurface of the catalyst. In any event, the silicon and barium arepresent in the form of their oxides, when combined therewith later inaccordance with the invention.

The bismuth molybdate catalyst composition of the invention may have thefollowing composition ranges, as long as the atomic ratio of bismuth tomolybdenum is above 1:3.

Element: Weight percent Bismuth 29.8478.08 Molybdenum 11.32-47.29 Oxygen996-2684 Phosphorus -2.40

This same composition may be expressed in the form of the followingempirical formula:

When silica is used as the support, the empirical formula is a b 12 c'(2)1 to 600 where a, b and c are as defined above.

When the silica is present at about 30 to 70 weight percent of the finalcomposition, the empirical formula is a b 12 c'( 2)30 to 150 where a, band c are as defined above.

To, this are to be added barium oxide and silicon oxides, as such or asformed in situ from other added barium and silicon compounds, so thatthe empirical formula of the promoted catalyst in accordance with theinvention corresponds to the following:

The values of a, b and c are in accordance with the definitions givenabove.

When the atomic ratio of bismuth to molybdenum BizMo is about 3 :4, theempirical formula is The values of b and c are as defined above.

When the silica is present as about 30 to 70 weight percent of the finalcomposition, the empirical formula is wehre a, b and c are as definedabove.

II. OXIDATION OF OLEFINS TO ALDEHYDES AND KETONES The reactants Thereactants used in the oxidation to oxygenated compounds are an olefin ormixture thereof and oxygen.

By the term olefin as used herein and in the appended claims is meantthe open-chain as well as cyclic olefins. Among the many olefiniccompounds which may be utilized in accordance with the process of theinvention, the following compounds are illustrative: propylene, butene-1, butene-2, isobutylene, pentene-l, pentene-2, 3-methy1- butene-l,Z-methyl-butene-Z, hexene-l, hexene-2, 4-rnethylpentene-l,3,3-dimethyl-butene-1, 4-methyl-pentene-2, octene-l, cyclopentene,cyclohexene, 3-methyl-cyclohexene, etc. This invention is directedparticularly to the oxidation of the lower alkenes (3 to 8 carbon atoms)but higher alkenes may also be utilized with efficacy. These 4.compounds and their various homologs and analogs may be substituted inthe nucleus and/or in the substituents in various degrees bystraight-chain alicyclic or heterocyclic radicals. The process of theinvention is applicable to individual olefins as well as to mixtures ofolefins and also to mixtures of olefins with the corresponding or othersaturated organic compounds.

The process of this invention is particularly adapted to the conversionof propylene to acrolein, isobutylene to methacrolein, alphaorbeta-butylene to methyl vinyl ketone, pentene-l or pentene-2 to ethylvinyl ketone and/ or pentene-3-one-2, 2-rnethyl-butene-2 to methylisopropenyl ketone, cyclopentene to cyclopentenone-2, and the like.

Straight-chain alpha-olefins of three or more carbon atoms, whenoxidized according to the process of the invention, tend to yield thesame products as the corresponding beta-olefins. Thus, as stated above,the alphabutylene, as well as beta-butylene, yields methyl vinyl kctone;and pentene-l, like pentene-2, yields ethyl vinyl ketone. It is believedthat this results from isomerization of the alpha-olefins to thebeta-olefins under the reaction conditions.

It is surprising that the vinyl type carbonylic products obtained by theprocess of this invention are not always those which would be expectedfrom the direct substitution of an oxygen atom for two hydrogen atoms inthe allyl position, i.e., for two hydrogen atoms attached to a carbonatom separated from the double bond by an intervening carbon atom. Forin the latter case beta butylene would form crotonaldehyde and notmethyl vinyl ketone. Instead, the reaction appears to be initiated atthe double bond and proceeds with the elimination of a hydrogen atom inthe allyl position and a change in position of the double bond.

The olefins may be in admixture with other hydrocarbons, for example, apropylene-propane mixture may constitute the feed. It is an advantage ofour process that the propane is not readily oxidized and passes throughthe reaction largely as an inert diluent. This makes it possible to useordinary refinery streams without special preparation.

Process conditions The temperature at which this oxidation is conductedmay vary considerably depending upon the catalyst, the particular olefinbeing oxidized and the correlated conditions of the rate of throughputor contact time and the ratio of olefin to oxygen. In general, whenoperating at pressures near atmospheric, i.e., 10 to p.s.i.g.,temperatures in the range of 500 to 1000 F. may be advantageouslyemployed. However, the process may be conducted at other pressures, andin the case where super atmospheric pressures, e.g., above 100 p.s.i.g.,are employed somewhat lower temperatures are feasible. In the case wherethis process is employed to convert propylene to acrolein, a temperaturerange of 750 to 850 F. has been found to be optimum at atmosphericpressure.

The apparent contact time employed in the process is not critical and itmay be selected from a broad operable range which may vary from 0.1 to50 seconds. The apparent contact time may be defined as the length oftime in seconds which the unit volume of gas measured under theconditions of reacton is in contact with the apparent unit volume of thecatalyst. It may be calculated for example from the apparent volume ofthe catalyst bed, the average temperature and pressure of the reactor,and the flow rates of the several components of the reaction mixture.The optimum contact time will, of course, vary depending upon the olefinbeing treated, but in the case of propylene the preferred apparentcontact time is 1 to 15 seconds.

A molar ratio of oxygen to olefin between about 5:1 to 05:1 generallygives the most satisfactory results. For the conversion of propylene toacrolein, a preferred ratio of oxygen to olefin is about 1:1. The oxygenused in the process may be derived from any source: however, air

appears to be the least expensive source of oxygen and it is preferredfor that reason.

We have also discovered that the addition of water to the reactionmixture has a marked beneficial influence on the course of the reactionin that it improves the conversion and the yield of the desired product.The manner in which water affects the reaction is not fully understoodbut the theory of this phenomenon is not deemed important in view of theexperimental results we have obtained. Accordingly, we prefer to includewater in the reaction mixture. Generally, a ratio of olefin to water inthe reaction mixture of 1:1 to 1:10 will give very satisfactory resultsand a ratio of 1:3 to 1:5 has been found to be optimum when convertingpropylene to acrolein. The water, of course, will be in the vapor phaseduring the reaction.

Inert diluents such as nitrogen, carbon dioxide, and saturatedhydrocarbons such as ethane, propane, and butane and pentane may bepresent in the reaction mixture.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed for the executionof the process. It may be operated continuously or intermittently andmay be a fixed bed with a pelleted catalyst or a so-called fluidized bedof catalyst. A fluidized catalyst bed simplifies problems of temperaturecontrol since coils through which water or other heat transfer medium iscirculated may be conveniently disposed in the bed to control thetemperature.

As stated above, pressures other than atmospheric may be employed inthis process but it is generally preferred to operate at or nearatmospheric pressure since the reaction proceeds well at such pressuresand the use of expensive high pressure equipment is avoided.

The reactor may be brought to the reaction temperature before or afterthe introduction of the vapors to be reacted. In large scale operation,it is preferred to carry out the process in a continuous manner and inthis system the recirculation of unreacted olefin and/ or oxygen iscontemplated. Periodic regeneration or reactivation of the catalyst isalso contemplated. This may be accomplished, for example, by contactingthe catalyst wth air at an elevated temperature.

The unsaturated carbonyl product or products may be isolated from thegases leaving the reaction zone by any appropriate means, the exactprocedure in any given case being determined by the nature and quantityof the reaction products. For example, the excess gas may be scrubbedwith cold water or an appropriate solvent to remove the carbonylproduct. In the case Where the products are recovered in this manner,the ultimate recovery from the solvent may be by any suitable means suchas distillation. The efficiency of the scrubbing operation may beimproved when water is employed as the scrubbing agent by adding asuitable wetting agent to the water. If desired, the scrubbing of thereaction gases may be preceded by a cold water quench of the gases whichof itself will serve to separate a significant amount of the carbonylproducts. Where molecular oxygen is employed as the oxidizing agent inthis process, the resulting product mixture remaining after the removalof the carbonyl product may be treated to remove carbon dioxide with theremainder of the mixture comprising any unreacted olefin and oxygenbeing recycled through the reactor. In the case where air is employed asthe oxidizing agent in lieu of molecular oxygen, the residual productafter separation of the carbonyl product may be scrubbed with anon-polar solvent e.g., a hydrocarbon fraction, in order to recoverunreacted olefin and in this case the remaining gases may be discarded.An inhibitor to prevent polymerization of the unsaturated products, asis well known in the art, may be added at any stage.

III. OXIDATION OF OLEFINS TO NITRILES The reactants The reactants usedare the same as in II above, plus ammonia. Any of the olefins describedcan be used.

In its preferred aspect, the process comprises contacting a mixturecomprising propylene, ammonia and oxygen with the catalyst at anelevated temperature and at atmospheric or near atmospheric pressure.

Any source of oxygen may be employed in this process. For economicreasons, however, it is preferred that air be employed as the source ofoxygen. From a purely technical viewpoint, relatively pure molecularoxygen will give equivalent results. The molar ratio of oxygen to theolefin in the feed to the reaction vessel should be in the range of0.5:1 to 3:1 and a ratio of about 1:1 to 2:1 is preferred.

The presence of the corresponding saturated hydrocarbons does not appearto influence the reaction to any appreciable degree, and these materialsappear to act only as diluents. Consequently, the presence of thecorresponding saturated hydrocarbons or other saturated hydrocarbons inthe feed to the reaction is contemplated within the scope of thisinvention. Likewise, other diluents such as nitrogen and the ovides ofcarbon may be present in the reaction mixture without deleteriouseffect.

Ammonia-olefin ratio The molar ratio of ammonia to olefin in the feed tothe reaction may vary between about 0.05:1 to 5: 1. There is no realupper limit for the ammonia-olefin ratio, but there is generally nopoint in exceeding the 5:1 ratio. At ammonia-olefin ratios appreciablyless than the stoichiometric ratio of 1:1, various amounts of oxygenatedderivatives of the olefin will be formed.

Significant amounts of unsaturated aldehyde or ketone as well as nitrilewill be obtained at ammonia-olefin ratios substantially below 1:1, i.e.,in the range of 0.15:1 to 0.75:1. Outside the upper limit of this rangeonly insignificant amounts of aldehyde or ketone will be produced, andonly very small amounts of nitrile will be produced at ammonia-olefinratios below the lower limit of this range. It is fortuitous that withinthe ammoniaolefin range stated, maximum utilization of ammonia isobtained and this is highly desirable. It is generally pos sible torecycle the olefin to the process, whereas the unconverted ammonia maybe recovered and recycled only with difiiculty.

H O-olefin ratio A particularly surprising aspect of this invention isthe effect of water on the course of the reaction. We have found thatthe presence of water in the mixture fed to the reaction vessel improvesthe selectivity and yield of the reaction as far as the production ofthe nitrile is concerned. Improvements on the order of several hundredpercent have been observed in the presence of water as compared tosimilar runs made in the absence of added water. Consequently, thepresence of water has a marked beneficial effect on this reaction, butreactions not including water in the feed are not to be excluded fromthis invention.

In general, the molar ratio of Water to olefin should be at least about0.25:1. Ratios on the order of 1:1 are particularly desirable but higherratios may be employed, i.e., up to about 10:1. Because of the recoveryproblems involved, it is generally preferred to use only so much wateras is necessary to obtain the desired improvement in yield. It is to beunderstood that water does not behave as an inert diluent in thereaction mixture. This conclusion has been verified by employing otherdiluents in the reaction mixture, such as propane and nitrogen. Nocorresponding improvement in yield and selectivity is observed with suchdiluents. Although the exact manner in which the water affects thereaction is not understood, it is clear that the water does have asignificant influence on the reaction.

One theory which has been postulated to explain the effect of water onthe reaction involves the phenomena occurring at the surface of thecatalyst. Water, because of its polarity, may assist in the desorptionof the reaction products from the surface of the catalyst. According toanother hypothesis, the water may change the nature of the catalyst atthe catalyst surface by affecting the acidity of the catalyst.Nothwithstanding the fact that either of these theories may be in error,the improved results occasioned by the use of water are evident and thetheory by which these results are to be explained is therefore to beconsidered immaterial.

Process conditions The temperature at which the reaction is carried outmay be any temperature in the range of from about 550 to about 1000 F.The preferred temperature range runs from about 800 to 950 F.

The pressure at which the reaction is conducted is also an importantvariable, and the reaction should be carried out at about atmospheric orslightly above atmospheric (2 to 3 atmospheres) pressure. In general,high pressures, i.e., above 250 p.s.i.g., are not suitable for theprocess since higher pressures tend to favor the formation ofundesirable by-products.

The apparent contact time employed in the process is not especiallycritical, and contact times in the range of from 0.1 to about 50 secondsmay be employed. The optimum contact time will, of course, varydepending upon the olefin being treated, but in general it may be saidthat a contact time of from 1 to seconds is preferred.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed in the executionof this process; The process may be conducted either continuously orintermittently. The catalyst bed may be a fixed bed employing a pelletedcatalyst or, in the alternative, a so-called fluidized bed of catalystmay be employed. The fluidized bed offers definite advantages withregard to process control in that such a bed permits closer control ofthe temperature of the reaction as is well known to those skilled in theart.

The reactor may be brought to the reaction temperature before or afterthe introduction of the reaction feed mixture. However, on a large scaleoperation it is preferred to carry out the process in a continuousmanner, and in such a system the recirculation of the unreacted olefinis contemplated. Periodic regeneration or reactivation of the catalystis also contemplated, andthis may be accomplished, for example, bycontacting the catalyst with air at an elevated temperature.

The products of the reaction may be recovered by any of the methodsknown to those skilled in the art. One such method involves scrubbingthe effluent gases from the reactor with cold water or an appropriatesolvent to remove the products of the reaction. In such a case, theultimate recovery of the products may be accomplished by conventionalmeans. The efficiency of the scrubbing operation may be improved whenwater is employed as the scrubbing agent by adding a suitable wettingagent to the water. Where molecular oxygen is employed as the oxidizingagent in this process, the resulting product mixture remaining after theremoval of the nit'riles may be treated to remove carbon dioxide withthe remainder of the mixture containing the unreacted propylene andoxygen being recycled through the reactor. In the case where air isemployed as the oxidizing agent in lieu of molecular oxygen, theresidual product after separation of the nitriles and other carbonylproducts may be scrubbed with a non-polar solvent, e.g., a hydrocarbonfraction, in order to recover unreacted propylene and in this case theremaining gases may be discarded. The addition of a suitable inhibitorto prevent polymerization of the unsaturated products during therecovery steps is also contemplated.

IV. OXIDATIVE DEHYDROGENATION OF OLEFINS TO DIOLEFINS The presentinvention also provides a process for the catalytic dehydrogenation ofnormal butylene, tertiary amylenes, and similar higher olefins having upto eight carbon atoms to the corresponding diolefins. In this processthe feed stream in vapor from containing the olefin to be dehydrogenatedand oxygen preferably is conducted over the catalyst at a comparativelylow temperature between about 750 and 1000" F., to obtain thecorresponding diolefin.

The reactants This process is capable of dehydrogenating normalbutylenes to butadiene and tertiary amylenes to isoprene, but it canalso be used to dehydrogenate normal amylenes to piperylene and higherolefins, e.g., hexenes, heptenes, and octenes, to the corresponding moreunsaturated products. The normal butylene can be butene-l or butene- 2,either cis or trans, or a mixture of normal butylenes, such, forexample, as can be separated from the products obtained in the crackingof petroleum oils or by the catalytic dehyrogenation of normal butane.The tertiary amylene can be any one or a mixture of the amylenes havingone tertiary carbon atom. The feed stock can contain diluents such asany paraffinic or naphthenic hydrocarbon having up to about ten carbonatoms. Propylene and isobutylene should not be included in amountsexceeding a few percent.

The feed stock is preferably catalytically dehydrogenated in thepresence of added steam, but this is not essential. Recommendedproportions of steam are between about 0.1 to 2 moles per mole ofreactant, but larger amounts can be used if desired.

Oxygen is also passed with the feed stock through the reaction zone.Recommended amounts are between about 0.3 and 2 moles per mole of olefinreactant. The stoichiometric quantity is 0.5 mole per mole of olefin. Itis referred to use a stoichiometric excess, e.g., about one mole permole of olefin. The oxygen may be supplied as pure or substantially pureoxygen, or air, or in the form of hydrogen peroxide.

It is generally preferred to maintain the concentration of oxygen in thereactant mixture entering the reactor below about 12% although somewhathigher concentrations may be used if the concentration of the olefinreactant is at least about 10% when operating at 30 p.s.i.g., at least15% when operating at 100 p.s.i.g., and at least about 20% whenoperating at 300 p.s.i.g. Thus when using pure oxygen, it is frequentlydesirable to dilute the mixture with an inert or substantially inertdiluent which may be steam, vapors of paraffin hydrocarbons, CO or thelike. On the other hand, if the amount of oxygen is such that it wouldconstitute more than about 12% of the reaction mixture the oxygen may beintroduced in increments, e.g., by injecting part of the oxygenseparately into the reaction zone.

Process conditions With the preferred catalyst the dehydrogenationbecomes substantial at about 340 C. The preferred reaction temperaturesare between about 400 and 550 C. Higher temperatures up to about 600 C.can be used, if means is provided to remove the exothermic heat ofreaction. The temperatures mentioned are those near the reactor inlet.If a fixed bed of catalyst is used the temperature downstream will be asmuch as C. higher.

The preferred pressure is near atmospheric, e.g., 5 to 75 p.s.i.a. Onthe other hand, higher pressures up to about 300 p.s.i.a. can be used,and have the advantage of simplifying the product recovery.

The process of the present invention allows a high space velocity, andthus, comparatively small reactors and catalyst can be used. Forexample, gasous hourly space velocities up to about 5000 may be employedwhile still obtaining reasonable conversions. Gaseous hourly spacevelocity, abbreviated CHSV, is defined as the volumes of reactant vaporcalculated under standard condition (STP) passed per hour per unitvolume of the catalyst bed. Generally, space velocities between about 50and 1000 are very satisfactory.

The contact of the feed vapors, oxygen and steam, if any, is preferablyeffected by providing the catalyst in the form of a fixed bed maintainedat the reaction temperature, and passing the feed vapors through thebed. In this method of operation the partial pressure of oxygen is high(maximum) at the inlet of the catalyst bed and declines towards theoutlet. The concentration of diolefin product, on the other hand, issubstantlally zero at the inlet of the bed and maximum at the outlet.This allows very high selectivities to be achieved. It is also possibleto use the catalyst in powder forms, but certain precautions should betaken. Thus, the powdered catalyst (e.g., passing a 100 mesh U.S.standard sieve) can be dispersed in the reactant vapor mixtures and thedispersion passed through the reaction zone.

The gaseous mixture issuing from the reaction zone may be quenched butthis is normally not essent1al. Ex cept in some cases when operating atthe upper limit of the recommended temperatures there is little tendencyfor side reactions to take place. The efliuent is preferably cooled byindirect heat exchange with the feed and then washed with dilute causticto neutralize the organic acids present and condense and remove thesteam. If air s used to supply the oxygen the remaining mixture 18preferably compressed and scrubbed with oil to separate the hydrocarbonsfrom the nitrogen, carbon dioxide, and carbon monoxide. The hydrocarbonmay be stripped from the oil and subject to an extractive distillationor a copper ammonium acetate treatment in the known manner to separateand recover the diolefin.

The following examples, in the opinion of the inventors, representpreferred embodiments of their invention:

EXAMPLE 1 A bismuth silicophosphomolybdate catalyst base was prepared bythe following procedure:

74 g. of an 85% phosphoric acid was added to 8330 g. of an aqueoussilica sol containing 30% silica. Next, 2800 g. of bismuth nitrate wasdissolved in a solution made by diluting 160 ml. of 70% nitric acid to1540 ml. with distilled water. The bismuth nitrate solution was thenadded to the silica sol. Next, 1360 g. of ammonium molybdate wasdissolved in 1540 ml. of distilled water, and this solution added to thesilica sol. The resulting catalyst slurry was dried in an oven at 200 F.for 24 hours and then calcined in a furnace at 800 F. for 24 hours.After cooling, the catalyst was ground into particles, and screenedthrough a mesh screen. A portion of the 8-10 mesh material was then madeinto tablets, while the remainder was retained for use as a control,designated hereinafter as Control A.

The final catalyst composition corresponded to the empirical formula BiPMo O -(SiO having the following composition:

Element: Weight percent Bismuth 24.2 Phosphorus 0.4 Molybdenum 14.8Silicon 23.4 Oxygen 37.2

This tabletted catalyst was then impregnated with promoters inaccordance with the invention, by the following procedure:

25.9 g. of barium acetate was dissolved in hot water and diluted up to420 ml. This hot solution was used to impregnate 400 g. of the tablettedcatalyst prepared as described above, dipping tablets of the catalystcontained in a wire basket in the solution for 4 minutes, then removingand draining them for 4 minutes. By thls procedure, 120 ml. of thebarium acetate solution was absorbed by the catalyst, equivalent to 4.4g. BaO. The wet catalyst was dried overnight, and a portion was setaside, for use later as Control B.

The remainder of the barium acetate-impregnated catalyst was impregnateda second time by the above method using a solution prepared by diluting206 g. of 30% fluosilicic acid solution to 420 cc. with water.

Another portion of the base catalyst (Control A), not previouslyimpregnated with barium acetate solution, was then impregnated with thefiuosilicic acid solution in the same way. This was marked Control C.

Both batches of the impregnated catalyst were dried at 120 C. overnight.

Controls B and C and the twice-impregnated catalyst of the inventionthen were calcined in air for 12 hours at 800 F. Finally, the threecalcined catalysts were ground and screened, to obtain a size fractionin the 8 to 10 mesh range.

Thus, Control B contained 1% added barium, Control C 1% added silicon,Control A neither, and the catalyst of the invention, 1% added bariumand 1% added silicon, together.

The promoted catalyst and the control catalysts A, B, and C withoutpromoters and with only one promoter were employed in a series ofexperiments, to determine catalytic effectiveness, using a fixed bedreactor, in the oxidative conversion of propylene and ammonia toacrylonitrile. A ml. catalyst charge was used in each run. Gases weremetered by Rotameter, and water was fed by a Sigma motor pump. The feedratios were held constant at H CaCHCH /NH /Air/N /H O l/ 1.5/ 12/4/08,and the contact time was held constant at 5 seconds. The reactiontemperature was varied from 850 to 910 F. in the series of runs carriedout. The percent conversion to acrylonitrile versus reaction temperaturefor each catalyst was determined for the twice impregnated catalyst ofthe invention. At the optimum temperature range of 890 to 900 F. 94% ofthe propylene feed Was converted, 77.6% being converted toacrylonitrile, 4.5% to acetonitrile, and the remainder to a mixture ofcarbon dioxide and hydrogen cyanide. The useful yield was 92.9%.

In contrast, Control A, the base catalyst without moters, at the optimumtemperature of 860'870 gave a total conversion of 93.2%, of which 63.4%was acrylonitrile, 13.0% acetonitrile and the remainder, carbon dioxideand hydrogen cyanide. The useful yield was 78.6%. The barium promotedControl B at the optimum temperature of 860870 F. gave a totalconversion of 70.8%, of which 51.4% was acrylonitrile, 8.4% acetonitrileand the remainder, carbon dioxide and hydrogen cyanide. The useful was85.0%. The silicon promoted Control C at the optimum temperature of900-910 F. gave a 78.6% total conversion, of which 58.4% wasacrylonitrile, 6.2% acetonitrile, 1.9% acrolein, 2.4% acetaldehyde, andthe remainder, carbon dioxide and hydrogen cyanide.

Thus, silicon alone and barium alone have a definite depressing effecton acrylonitrile formation, While the two together materially enhancethe catalytic effect, as compared to the base catalyst.

The barium and silicon promoted catalyst was next employed in fixed bedform for the conversion of propylene to acrolein. During the reactionthe reactor was maintained at a temperature of 825 F. at atmosphericpressure. The contact time with the catalyst was approximately onesecond. The feed molar ratios were air/H O/ propylene/nitrogen,5/6/1/32. Approximately 56% of the propylene feed was converted toacrolein and about 31% of the propylene was unreacted. This unreactedmaterial could be recycled. The remainder of the product consisted ofcarbon oxides, minor amounts of low molecular weight carbonyliccompounds, and organic acids.

EXAMPLE II The bismuth silicophosphomolybdate catalyst of Expro- F.

before, was the base catalyst. Control B was prepared in the same way,but using a barium acetate solution containing 77.7 g. of bariumacetate, three times the previous concentration, thus giving a catalystcontaining 3% added barium, instead of 1%. Control C was identical toExample I, and the catalyst of the invention contained 3% added bariumand 1% added silicon, as the oxides.

The catalysts were used in the conversion of propylene and ammonia toacrylonitrile, using the reactor of Example I.

The catalyst of the invention at the optimum temperature of 875 F. andair/NH /H O/N ratio of /1/4/5, and a contact time of 8 seconds, gave atotal conversion of 99.9% of which 75.4% was acrylonitrile, 4.5%acetonitrile, 0.9% acrolein, and the remainder carbon dioxide andhydrogen cyanide. The total useful yield was 79.9%. This is to becompared to the base catalyst, which under the Example I conditions gavea 63.4% conversion to acrylonitrile, 13.0% conversion to acetonitrile,and the remainder carbon dioxide and hydrogen cyanide, giving a totalconversion of 93.2% and a useful conversion of 78.6%. Control B at860870 F. and the conditions of Example I gave a total conversion of78.9%, of which 61.0% was acrylonitrile, 9.5% acetonitrile, and theremainder carbon dioxide and water, a total useful yield of 87.8%.Control C under the Example I conditions at 900910 F. gave a 78.6% totalconversion, of which 58.4% was acrylonitrile, 6.2% acetonitrile, 1.9%acrolein, 2.4% .acetaldehyde and the remainder carbon dioxide andhydrogen cyanide.

The catalyst of the invention containing 3% added barium and 1% addedsilicon was also used in the conversion of propylene to acrolein in afixed bed. During the reaction, the reactor was maintained at atemperature of 850 F. at 6 p.s.i.g. The apparent contact time with thecatalyst was approximately 2.8 seconds. The feed molar ratios werepropylene/ air/H O/ nitrogen, 1/11/2/12. Approximately 53% of thepropylene feed was converted to acrolein. The total conversion was 79.7%of the propylene feed, the remainder consisting of 0.5% acctaldchyde,2.9% acrylic acid, 1.3% acetic acid, and carbon oxides.

EXAMPLE III A bismuth silicomolybdate catalyst was prepared followingthe procedure given in Example 1, except that no phosphoric acid wasadded to the base catalyst slurry. This catalyst was then impregnatedwith barium acetate and fluosilicic acid solution, as described inExample I, and the resulting catalyst used in the oxidation of propyleneas in Example I, in comparison with the base catalyst. The promotedcatalyst gave an increase of approximately 10% in the conversion ofpropylene to acrylonitrile, as compared to the base catalyst.

Each of the above examples utilizes the barium and silicon-promotedcatalyst of the invention in comparison against the base catalyst in theoxidation of olefins to oxygenated hydrocarbons, e.g., propylene toacrylonitrile. It will be understood that the promotional effect is alsoevidenced in the oxidative dehydrogenation of olefins to diolefins, suchas butene to butadiene, and amylenes to isoprene, as described in U.S.Patent No. 2,991,320 to I-Iearne and Furman, patented July 4, 1961.

EXAMPLE IV Butene-l was dehydrogenated to butadiene using the barium andsilicon promoted catalyst of Example I in a fixed bed reactor.. Thebutene-l feed was mixed with air and water in the molar ratio butene/air/ water 1/ 8/ 4 and preheated to 850 F. The temperature in thereactor was held at 850860 F. The residence time in contact with thecatalyst was six seconds. 300 ml. of catalyst was used. The conversionper pass to 1,3-butadiene was 74%, together with 6.3% oxygenatedproducts, the balance being carbon oxide.

12 EXAMPLE V Trans-butene-2 was dehydrogenated to butadiene using thebarium and silicon promoted catalyst of Example I in admixture with airand steam. The reactor temperature was held at 835-845 F. and the molarratios butene/air/ water at 1/8/4. The residence time in contact with300 ml. of catalyst was four seconds. A per pass conversion to1,3-butadiene of 76% was obtained, the balance of the product beingcarbonyl compounds and carbon oxides.

EXAMPLE VI Butene-l was dehydrogenated to butadiene using the 3%barium-1% silicon promoted catalyst of Example II in a fixed bedreactor. The butene-l feed was mixed with air and water in the molarratio, butene/air/water, 1/ 8/ 4. The temperature in the reactor washeld at 870 F., and the apparent contact time was 6 seconds. Thereaction was conducted at atmospheric pressure. 300 ml. of catalyst wasused. The conversion per pass to 1,3-butadiene was together with 7%oxygenated products, the balance being carbon oxides.

All percentages in the specification and claims are by weight, in thecase of the catalyst composition, and by volume in the case of gases.

We claim:

1. The process for the dehydrogenation of monoolcfins to diolefins whichcomprises contacting the olefin and oxygen in the vapor phase at atemperature at which dehydrogenation proceeds with a catalyst consistingessentially of oxides of bismuth and molybdenum as the essentialcatalytic ingredients, the bismuth oxide being present in an amount tofurnish a bismuth to molybdenum BitMo atomic ratio of above 1:3,promoted by a mixture of oxides of barium and silicon, in the proportionof about 1 to about 5%, calculated as barium, and about 1 to about 10%calculated as silicon.

2. The process in accordance with claim 1, in which the olefin is abutene.

3. The process in accordance with claim 1, in which the catalyst alsoincludes phosphorus in an amount up to about 5% by Weight.

4. The process in accordance with claim 1, in which the catalyst has acomposition corresponding to the empirical chemical formula:

72.5-97%(Bi,P Mo O -16%BaO-221.5%Si0 where a is a number within therange from about 4 to 36, b a number within the range from 0 to 2, and cis /zn-a-l-Vzm-b-H/zp-lZ, wherein n, m and p are the average valences ofbismuth, phosphorus and molybdenum, respectively, in the catalyst.

S. The process in acordance with claim 1, in which the catalyst issupported on silica.

6. The process for the dehydrogenation of monoolcfins to diolefins whichcomprises contacting an olefin having from four to eight carbon atomsand oxygen in the proportion of from about 0.3 to about 2 moles per moleof olefin at a temperature at which dehydrogenation proceeds within therange from about 750 to about 1000 F., with a catalyst consistingessentially of oxides of bismuth and molybdenum as the essentialcatalytic ingredients, the bismuth oxide being present in an amount tofurnish a bismuth to molybdenum BizMo atomic ratio of above 1:3,promoted by a mixture of oxides of barium and silicon, in the proportionof about 1 to about 5 calculated as barium, and about 1 to about 10%,calculated as silicon.

7. The process in accordance with claim 1, in which the olefin is abutene.

References Cited UNITED STATES PATENTS 2,991,320 7/1961 Hearne et al260-680 3,044,966 7/1962 Callahan et al. 252437 3,161,670 12/1964 Adamset al. 260680 X PAUL M. COUGHLAN, 1a., Primary Examiner.

1. THE PROCESS FOR THE DEHYDROGENATION OF MONOOLEFINS TO DIOLEFINS WHICHCOMPRISES CONTACTING THE OLEFIN AND OXYGEN IN THE VAPOR PHASE AT ATEMEPRATURE AT WHICH DEHYDROGENATION PROCEEDS WITH A CATALYST CONSISTINGESSENTIALLY OF OXIDES OF BISMUTH AND MOLYBDENUM AS THE ESSENTIALCATALYTIC INGREDIENTS, THE BISMUTH OXIDE BEING PRESENT IN AN AMOUNT TOFURNISH A BISMUTH TO MOLYBDENUM BI:MO ATOMIC RATIO OF ABOVE 1:3,PROMOTED BY A MIXTURE OF OXIDES OF BARIUM AND SILICON, IN THE PROPORTIONOF ABOUT 1 TO ABOUT 5%, CALCULATED AS BARIUM, AND ABOUT 1 TO ABOUT 10%,CALCULATED AS SILLICON.